The present invention relates to air heaters and more particularly to an indirect-fired air heater of the portable type suitable for field use to heat both personnel and equipment and a method of heating air.
It is generally well known in the portable heater art to provide a forced air heater which includes an outer casing having a smaller combustion drum disposed therein which defines a plurality of air heating passages extending through the heater between the drum and the casing, the heater including a blower to force air through the heating passages and a burner to direct flame in the combustion drum toward the downstream end where resulting gases are evacuated. More recently attempts have been made to eliminate the vanes and baffles required at the downstream end of the drum to obtain sufficient heat transfer and to eliminate concomitant pressure drop brought about by such vanes and baffles. In U.S. Pat. No. 4,309,978, more recently issued on Jan. 12, 1982 to Charles R. Hensiek et al, a portable heater structure was disclosed which reversed the combustion gas flow at the downstream end of the combustion drum to form a flow of hot combustion gases moving toward discharge ports at the upstream end of the combustion drum, thus more effectively utilizing the entire length of the heater for heat exchange purposes and obtaining complete combustion without corrosive carbon deposits within the drum. To accomplish this and at the same time support the combustion drum within the outer casing, a particular type of ribbed drum was provided with the ribs abutting the casing and sometimes leading to "hot spots" at the areas of abutment, gathering particulate matter and interfering with heat exchange flow. Further, the manufacturing and assembly steps required were often extensive and complex and hardly economical.
The present invention, recognizing the desirablity of reversing combustion gas flow at the downstream end of a combustion drum to form a flow of hot gases toward the upstream end of the combustion drum and at the same time recognizing the limitations of past structure to accomplish the same, provides an improved forced air heating apparatus which allows for the prompt and efficient heating of large volumes of air with a minimum of flow turbulence and pressure drop, assuring efficient utilization of radiant and convective heat energy and, at the same, requiring a minimum number of steps and parts in both manufacture and assembly. In addition, the present invention provides a novel method of supporting a combustion drum within the outer casing of a portable heater without sacrificing smooth, laminar heat exchange flow and without creating possible areas of undue wear, undesirable hot spots and unwanted crevices for particulate concentrations in the outer casing.
Various other features of the present invention will become obvious to one skilled in the art upon reading the disclosure set forth herein.